This invention relates generally to the solar panel art and, more particularly, to an improved solar panel with a hardened aluminum foil back layer.
Solar panels having front layers of glass or other rigid transparent material have been provided with aluminum foil layers to hermetically seal the back of the panel. As far as applicant is aware, the use of aluminum foil in such panels has been limited to common annealed or dead soft foil of the type used in most packaging applications. The foil is typically bonded to the transparent outer layer through a plurality of solar cells and at least one dielectric layer. Because glass has a much lower thermal expansion coefficient than the metal used to form the foil layer, substantial stresses are placed on the foil when the solar panel is exposed to extreme temperatures during use. In many panels using annealed aluminum foil layers, the stresses applied to the foil during thermal cycling are sufficient to stretch it beyond its elastic limit. The foil can then buckle and pull away from the other components of the panel, or can form pin holes and stress cracks which spoil the hermetic sealing properties of the foil.
While some of the problems discussed above are eliminated when steel foil is used in the back layer, it is much more expensive than aluminum foil and is less readily available commercially. Steel foil is also more difficult to form into the thin sheets desired for use in solar panels and has a much greater tendency to corrode.
Therefore, in many applications it is desirable to provide a solar panel having an inexpensive sealing back layer which will not buckle in use when placed in conjunction with a front layer having a relatively low thermal expansion coefficient.